Enhancing the water repellency of wood surfaces by atmospheric pressure cold plasma deposition of fluorocarbon film

Abstract

In this study, fluorocarbon thin films were deposited on the surface of white spruce and Brazilian cedar woods via atmospheric pressure dielectric barrier discharge in the afterglow mode with octafluoropropane gas. A pre-treatment with oxygen plasma was introduced before the thin film deposition to determine if this plasma condition could increase the wood nano/micro roughness, helping to improve the hydrophobicity of the surface. The optimal conditions of water repellency for both woods were examined in terms of their resistance to aging in controlled conditions. The water contact angle measurements showed a hydrophobic surface with a stable angle for both woods. X-ray photoelectron spectroscopy reveals the presence of CF, CF2 and CF3 functional groups after the Ar/C3F8 plasma, especially for longer treatments. The open-air system of the plasma reactor leads to the simultaneous fluorination and incorporation of oxygen-containing groups. The pre-treatment of oxygen plasma increases the wood roughness; however, the chemical attachment of oxygen molecules is more significant, negatively affecting the degree of repellency of the plasma-coated woods. On the other hand, the fluorocarbon deposition increases the wood roughness and creates a hydrophobic surface simultaneously. Even with partial defluorination after aging, both plasma-coated woods retain a similar degree of water repellency, which partially avoid chemical reorganization of their surface due to environmental exposure.